a) Field of the Invention
The present invention relates to a novel thermoplastic resin composition which can be utilized as a material for producing molded articles by injection molding, extrusion molding or the like process.
b) Prior Art
Generally, polyphenylene ethers are excellent in heat resistance, hot water resistance, dimension stability, and mechanical and electrical properties. On the other hand, they have disadvantages; for example, they show unsatisfactory moldability due to their high melt viscosity, poor chemical resistance, and low impact resistance.
Known methods for improving moldability by lowering the melt viscosity of polyphenylene ethers while maintaining their excellent properties include use of a mixture of a polyphenylene ether and a polystyrene resin. However, these known methods still fail to improve chemical resistance.
On the other hand, propylene polymers are not only excellent in various properties such as moldability, toughness, water resistance, chemical resistance, etc., but also they have low specific gravity and are cheap in cost; they have been widely used as a material for preparing various molded articles, films, sheets, etc.
However, the propylene polymers have defects or points which need to be improved in heat resistance, rigidity, impact resistance, coatability, adhesiveness, etc., which presents an obstacle in developing new practical utility. In particular, improvement in the heat resistance and impact resistance thereof is strongly desired.
Naturally, it may be expected to blend a polyphenylene ether and a propylene polymer to prepare a resin composition which could have the advantages of both polymers and which could have improved moldability and impact resistance, and thus a wide possibility of new applications would be open.
Blending a polyphenylene ether with a propylene polymer, however, actually gives rise to a resin composition in which the miscibility of both polymers is poor so that molded articles obtained from such a blend as by injection molding suffers phase separation between the polyphenylene ether and the polypropylene, thereby providing articles having extremely poor appearance and poor mechanical properties, which are unsatisfactory for practical purposes.
On the market, there is increasing demand for resin compositions which retain excellent heat resistance derived from polyphenylene ether and in addition, high impact resistance and excellent weatherability.
A method for improving the miscibility between a polyphenylene ether and a propylene polymer is known, as described in Japanese Patent Application No. 63-33445, in which method a polyphenylene ether is blended with a propylene polymer grafted with a styrene based monomer by graft copolymerization. This method, however, fails to provide a composition having excellent impact resistance.
As described in Japanese Patent Publication (Kokai) No. 57-108153, a method is known in which polyphenylene ether is blended with a copolymer of an olefin and glycidyl methacrylate and/or glycidyl acrylate, and a method is also known in which polyphenylene ether is blended with a rubbery substance in order to improve its impact resistance. However, both of these methods fail to provide resin compositions which have satisfactory heat resistance and impact resistance.
In view of the above points, the present inventors have studied intensively and extensively in order to develop effective technology for improving the properties of resin compositions made of polyphenylene ethers and propylene polymers, and as the result they have completed the present invention.